Most standard jet engines are made up of at least an air intake, a series of compressors, a combustion chamber, a series of fans and/or turbines and an exhaust nozzle. In a typical jet engine, air comes into the front of the engine and is compressed by the compressors. The air then passes into a combustion chamber where fuel is added and ignited. This expanding air is then used to drive a series of turbines. These turbines are connected to compressors by shafts and hence drive them. The air then travels out of the back of the engine to provide thrust. A turbine consists of a number of blades placed around a shaft. There are two essential types, fans and compressors. In a fan the blades are quite long and slender while in a compressor they are short and compact.
Most all jet engines and the like are prone to vibration from the rotating fan and compressor parts. The vibration arises because often the center of mass of each disc rotating assembly may be slightly displaced from the center of rotation. Moreover, the shaft may also suffer from slight misalignment and center of mass offsets too. Thus, when the engine rotates, these imbalances cause the individual components to vibrate. Differences between the levels of vibration of each part may aggravate the resulting movement of the engine etc. The vibration is typically transmitted through the aircraft structure generating corresponding noise and vibration in fuselage and cabin of the aircraft. Many times such vibrations and noises often cause passenger and crew discomfort. A need exists to delete such vibrations, especially in flight, and transmit this information for calculating and determining real time balancing solutions to minimize the vibration and noise relating to the engine and vibrations detected within the aircraft cabin caused by such engine vibrations.
Many commercial airline carriers and other aviation related industries frequently monitor the structural health, integrity and status of their aircraft and more specifically the life blood of the aircraft—its engines. Such structural health and status information is frequently utilized to determine the current performance of an engine in addition to determining if engine maintenance is required. There are presently many systems that monitor aircraft and aircraft engine performance and health factors.
However, there exist no systems and methods for measuring, monitoring, storing, and transmitting data containing vibration and balance information that exist or occur during flight especially those relating to the N1 low pressure fans of a jet engine. Present systems require the aircraft to be on the ground and on open tarmac to perform adequate engine runs utilizing externally attached monitoring equipment to determine and analyze vibration and balancing problems of a jet engine. Many times, the engine must be fully dismounted from the aircraft wing and installed in an engine test cell facility to adequately analyze such problems.
There are currently three methods to collect data for balancing fan systems on modern jet aircraft such as the Boeing 757. One such method uses externally mounted instrumentation to collect the necessary vibration data for calculating a balance solution. An example of such externally mounted instrumentation is that found in the PBS4000 and PBS4100 series vibration and balancing systems manufactured by MTI Instruments, Inc. of Albany, N.Y.
A second method utilizes the internal solution capability of certain aircraft vibration monitoring units. However, many times this option tends to dramatically increase cost factors to modify current airline fleets to integrate this system with in place equipment. However, many carriers still opt to make use of such vibration detection and monitoring units.
A third method for such “on the ground” engine test runs, and one of the primary methods for accomplishing a fan system balance solution, is achieved utilizing what is known to those skilled in the art as the “3-shot plot” method and is described in further detail hereinbelow.
The balancing of fans is a regular maintenance operation for the airlines. Typically an engine will be dismantled and tested for defects, and any faulty blades replaced by new ones. The turbine then needs to be reassembled and balanced, an operation complicated by differences in blade weights. The overall balancing can be a time consuming task, particularly for those engines where the fan must be dismantled and reassembled whenever blades are interchanged. The fan balancing is a major part of the maintenance operation. When maintenance is carried out on fans or ‘spools’ (banks of blades on a shaft) they must be dynamically balanced by the addition of small correction weights before being reassembled into their modules. This dynamic balancing requires that the spools be loaded into a test bed which then spins the spools up to normal running speed. External equipment with special sensors are used to register any imbalance or vibration. From the vibration patterns, it is possible to calculate the location of the mass center and to indicate where correction weights should be placed. Once the engine has been fully reassembled it too must be dynamically balanced. If such an imbalance is found, it is generally solved by rotating the modules with reference to each other. This allows the individual imbalance forces to be aligned to reduce the overall imbalance. The blades on an individual turbine are all slightly different in weight due to manufacturing variation. As a consequence, different orders of placement of the blades around the turbine will give rise to different mass centers. The determination of a correct ordering of blades is an important engineering problem for a number of reasons. First, there is a limit on the number of correction weights that can be used in the subsequent dynamical balancing of the fan.
In addition, imbalance of rotors, such as large compressor fans of jet engines, can occur when part, or whole, of a fan blade becomes detached from the fan disc while the engine is running. When a blade is lost the rotor experiences a large out-of-balance load which causes the rotor to orbit bodily about its original axis of rotation. Because of manufacturing inaccuracies, variations occur in the weights of the blades that can, in turn, lead to significant out-of-balance forces on the engine. The overall time and cost required for balancing can be significantly decreased if the best balancing solution can be determined by integrity sensors and equipment already available on many aircraft, but in addition being able to transmit via communication links and equipment to ground receivers that calculate balance solutions for use by maintenance upon landing.
As such, many jet engine original equipment manufacturers (OEMs), jet engine service providers and commercial aviation companies have desired a system and method to monitor, record, transmit and calculate fan system balance solutions of an aircraft engine in real-time and be able to make such solutions available to an awaiting mechanic. Many current systems found on modern commercial aircraft monitor various aircraft and engine status and performance. Such status and performance data are frequently recorded and transmitted via an Aircraft Communications Addressing and Reporting System (ACARS) using a communication data link. Many times such data relating to the aircraft engine result in limited engine analysis because only certain parameters of the engine performance had been monitored, stored, transmitted and used and the data never given a complete picture or historical indication of engine vibration and balance performance in-flight.
Current systems and methods of recording performance of an aircraft engines use a ground data link unit that interfaces with numerous components of the aircraft. Modern aircraft currently operated by the commercial airline industry employ airborne data acquisition equipment, such as a digital flight data acquisition unit (DFDAU) as a non-limiting example, which monitor signals supplied from a variety of transducers distributed throughout the aircraft, and provide digital data representative of the aircraft's flight performance based upon such transducer inputs. As flight performance data is obtained by the DFDAU equipment, it is stored in an attendant, physically robust, digital flight data recorder (DFDR—commonly known as the aircraft's “black box”), so that in the unlikely event of an in-flight mishap, the DFDR can be removed and the stored flight performance data analyzed to determine the cause of the mishap.
However, there exists a need for a system and method that utilizes the aircraft's onboard acquisition equipment and sensors, without significant modification, to monitor, collect, record, and transmit certain flight phase results of data variables and parameters of engine vibration information specifically relating to N1 compressor stage fan vibrations during flight and on the ground via at least radio waves to ground stations for processing and calculation of real-time fan balance solutions.
In addition, there exists a need for making readily available such N1 stage real-time fan balance solutions to industry know-how so as to be readily prepared to repair any known imbalances discovered during flight or on ground test runs but while utilizing minimum manpower, time, and fuel as compared to current methods.